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The Early Devonian Eurypterid Grossopterus Overathi (Gross, 1933) from Overath, Germany

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The Early Devonian Eurypterid Grossopterus Overathi (Gross, 1933) from Overath, Germany Mitt. Mus. Nat.kd. Berl., Geowiss. Reihe 5 (2002) 93-104 10.11.2002 The Early Devonian eurypterid Grossopterus overathi (Gross, 1933) from Overath, Germany Jason A. Dunlopl, Simon J. Braddy2 & Erik Tetlie2 With 6 figures Abstract The holotype and only known specimen of the eurypterid (Chelicerata: Eurypterida) Grossopterus overathi (Gross, 1933) from the Early Devonian (Siegennian) of Overath, north-west Germany is redescribed. Based on comparisons with other eurypterid taxa we interpret G. overathi as having a well-preserved type B genital appendage, which exhibits two apomorphic character states: (1) a furca fused into a single, spatulate plate and (2) marginal serrations near the distal end of the appendage. Grossop- terus is assigned to the family Hughmilleriidae, but its carapace resembles that of the larger Slimoniu acuminatu (Salter, 1856) (Slimoniidae). A provisional phylogenetic analysis resolves Grossopterus as the sister group of (Slimonia + Pterygotoidea). The large pterygotids, in particular, have been suggested as significant predators on early vertebrates and hypotheses about eurypterid-fish co-evolution are reviewed, in particular Romer’s proposal that dermal annour in fish evolved in response to eurypterid predation. Key words: Devonian, north-west Germany, Overath, Eurypterida, Grossopterus, Genital appendage, fish, co-evolution. Zusammenfassung Der Holotyp - das einzig bekannte Exemplar - des Eurypteriden (Chelicerata: Eurypterida) Grossopterus overathi (Gross, 1933) aus dem friihen Devon (Siegennian) von Overath im nordwestlichen Deutschland wird wieder beschrieben. Basierend auf Vergleichen mit anderen Eurypteriden-Taxa interpretieren wir G. overathi als Trager eines Typ B-Anhanges, wobei zwei apomorphe Merkmalszustande vorliegen: (1) die Furca ist zu einer einzigen, spatelformigen Platte verschmolzen, und (2) der Seitenrand nahe des distalen Endes des Genitalanhanges ist gezahnt. Grossopterus wird zur Familie der Hughmilleriidae gestellt, aber der prosomale Dorsalschild ahnelt der groljeren Slimoniu acuminata (Salter, 1856) (Slimoniidae). Eine vorlaufi- ge phylogenetische Analyse zeigt Grossopterus als Schwesteruppe von (Slimonia + Pterygotoidea) auf. Besonders die groljen Pterygotiden wurden als signifikante Pradatoren von friihen Vertebraten gehandelt, und Hypothesen zur Eurypteriden-Fisch Koevolution werden iiberpriift, speziell Romers Vorschlag, dass die dermale Panzerung von Fischen als Antwort auf die Pradation durch Eurypteriden evolvierte. Schliisselworter: Devon, Nordwestdeutschland, Overath, Eurypterida, Grossopterus, Genitalanhang, Fische, Co-Evolution. Introduction eurypterid material. Stormer (1934) redescribed E. (?) overathi in some detail and established a In 1933 Walter Gross described a fauna of fish new genus for it, Grossopterus Stormer, 1934, and eurypterids collected by himself and Walter which he named after Gross and diagnosed on Schriel from Early Devonian sediments at a characters such as the carapace shape with in- quarry in Overath, near Cologne, Germany. curving lateral margins and the shape of the Among the fossils figured by Gross (1933) were genital appendage (see also below). In the same fragments of pterygotid eurypterids and an al- paper an incomplete specimen from the Middle most complete specimen which he named Eur- Devonian of the USA, Pterygotus inexpectans ypterus (?) overathi Gross, 1933. Subsequently, Ruedemann, 1921 was tentatively referred to W. Gross invited Leif Stcwmer to re-examine this this new genus. G. overathi was also figured in Museum fir Naturkunde, Institut fir Systematische Zoologie, InvalidenstraBe 43, D-10115 Berlin, Germany. E-mail: [email protected] Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol, BS8 lRJ, UK. E-mail: [email protected] [email protected] Received February 2002, accepted May 2002 0 2002 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1435-1943/02/0511-0093 $17.50+.50/0 94 Dunlop, J. et al., Redescription of Grossopterus the Treatise on Invertebrate Paleontology (Stgr- overathi could, therefore, be a basal member of mer 1955). the lineage which led to some of the largest eur- Work on eurypterid systematics was domi- ypterids; arthropods up to two metres long nated in the mid- 20th century by Leif Stgrmer, which are popularly perceived as having been Erik Kjellesvig-Waering and Charles Waterston. significant predators on early vertebrates. As at However, since the late 1970s most publications Overath, Siluro-Devonian eurypterids are often on eurypterids have been palaeobiological, to- found in association with fish, leading Romer gether with the descriptions of a few new taxa. (1933) to speculate that eurypterids exerted a se- With the exception of Tollerton’s (1989) valuable lective pressure for the development of verte- compilation of genera and suprageneric taxa, brate dermal armour. This hypothesis is dis- there have been few recent systematic revisions. cussed below in the light of recent critical Tollerton (1989, table 8) recognised over sixty remarks. valid eurypterid genera (excluding the unusual cyrtoctenids), at least seven of which could not be placed within his familial scheme because Material they were based on incomplete, or even frag- mentary, material. Indeed, eurypterid systematics Both Gross (1933) and Stormer (1934) cited the type reposi- tory of G. overathi as the Geologisches Landesmuseum Ber- is plagued by taxa raised on isolated head lin. The Landesmuseum material now forms the palaeontolo- shields (Ruedemann 1921), telsons (Kjellesvig- gical collection of the Museum fur Naturkunde, Berlin (MfN) Waering 1951, 1973) or the dentition of disarticu- and the holotype, and only specimen, of G. overathi is held here in the arthropod palaeontology collections under the lated chelicerae (Kjellesvig-Waering 1964), and repository number MB.A. 2a+b (i.e. part and counterpart). on names assigned to non-descript stains and The holotype of G. overathi was examined under a stereomi- other non-eurypterid material; see e.g. Toller- croscope with a camera lucida attachment used to draw the genital region in detail. Specimens were compared to other ton’s (1994) comments on many of the Ordovi- eurypterid taxa, principally Battoeurypterus Stprrmer, 1973, cian taxa from New York State. Erettopterus Salter, 1859, Sfimonia Page, 1856 and Hughmil- Tollerton’s (1989) typological scheme of higher leria Sarle, 1903, based on the literature and material in var- ious collections including the MfN, the Natural History Mu- systematics has not been translated into a parsi- seum, London, the National Museum of Scotland, Edinburgh mony-based model of eurypterid evolution. The and the Sedgwick Museum, Cambridge. Tenninology follows only comprehensive cladistic analyses are in the Stprnner (1955) and Tollerton (1989) and also Selden (1981) for the appendages and Braddy & Dunlop (1997) for the unpublished theses of Plotnick (1983) and Brad- genitalia. dy (1996); a version of Plotnick’s cladogram was figured by Beall & Labandeira (1990), but with- out accompanying discussion. There is also a Geological Setting published analysis of the pterygotid genera by Plotnick & Baumiller (1988). Redescriptions of Schriel (1933) described the stratigraphic and some of the less well known or taxonomically tectonic setting of the Overath fossils. The fish complex genera are an important prerequisite and eurypterids, including G. overathi, were col- for scoring characters into future phylogenetic lected from a 10-20cm thick unit (Gross 1933) studies; see also comments in Braddy (2000). in the Heider quarry which belongs to the In this paper we redecribe G. overathi as part Wahnbach-Schichten of the Rheinische Schiefer- of a wider systematic revision of the Eurypteri- gebirge and was noted by Schriel as the most da. In contrast to StQrmer (1934), we reinterpret important locality for dating this Early Devonian its genital appendage as a type B appendage, but formation in the Overath region. According to one in which the distal furca has fused into a both Schriel (1933) and more recently Schweit- spatulate plate with marginal serrations. This di- zer (1983: table 4) the Wahnbach-Schichten is agnostic character appears to be autapomorphic mid- to late Siegennian in age; a date also given for the genus. Grossopterus shares potential on the G. overathi labels. The associated fish fau- characters with members of the Hughmilleriidae, na from the Heider quarry includes agnathans, to which it was originally assigned (Stormer elasmobranchs and crossopterygians. A large 1955, Tollerton 1989), but also with the larger amount of (mostly unidentified) plant material Slirnonia acurninatu (Salter, 1856) (Slimoniidae). was also reported (see Gross 1933 for details). Here, we present a preliminary phylogenetic analysis based on selected taxa, the results of which imply that G. overathi, S. acurninata and the pterygotid eurypterids may form a clade. G. Mitt. Mus. Nat.kd. Berl., Geowiss. Reihe 5 (2002) 95 Fig. 1. Grossopterus overathi (Gross, 1933). MB.A. 2a + b. From the Early Devonian (Siegennian) Wahnbach-Schichten, col- lected at the Heider quarry near Overath, Nordrhein-Westfalen, Germany. A. Dorsal surface showing prosomal dorsal shield (or carapace), most of the opisthosoma and some appendages. B. Ventral surface showing the metastoma, some coxal ele- ments and an incomplete opisthosoma with a prominent genital appendage. Scale bar equals 20 mm. Morphological interpretation The part has a split
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